


Super Sister

by Irhaboggle



Category: Supergirl (TV 2015)
Genre: Danvers, Danvers Sisters, Disaster, Funny, Harun-El, Humor, Kryptonian, Minor Alex Danvers/Maggie Sawyer, One Shot, Short, Sister - Freeform, Sisterly, Sisterly Love, Superpowers, alien - Freeform, harun el, harunel, hero - Freeform, super, superpower, superpowered
Language: English
Status: Completed
Published: 2019-07-23
Updated: 2019-07-23
Packaged: 2020-07-12 00:57:30
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 5,121
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19937389
Author URL: https://archiveofourown.org/users/Irhaboggle/pseuds/Irhaboggle
Summary: When Kara catches a cold that temporarily mutes her powers, she sends in her sister (drugged up on Harun-El) to act as her Supergirl stand-in. Sadly, being a hero is harder than it looks and Alex proves that she has a lot to learn before she masters the art of keeping her superpowers in check. Good thing Kara is there to nag- err, help, her on every step of the way!





	Super Sister

**Author's Note:**

  * For [Snorlax891](https://archiveofourown.org/users/Snorlax891/gifts).



"Ok, you are having way too much fun with all that increased physical prowess," Kara sighed, pinching the bridge of her congested nose as she watched Alex on the large monitor in the main part of the DEO. At the moment, the older Danvers sister was going all out, smashing a boulder to smithereens with her bare hands. She looked beyond exhilarated.

Due to a rare (but thankfully relatively harmless) sickness Kara contracted, she was rendered borderline human. Because of that, she wasn't able to perform her Supergirl duties. Alex was more than happy to take over, using some leftover Harun-El to give her a boost. Now she was out in the middle of nowhere, practicing with her newfound powers for the first time ever. Kara, meanwhile, stayed behind at the DEO, trying to recover from her sickness while also keeping tabs on Alex. As she had said, Alex seemed to be having far too much fun with the Harun-El's strength booth. She was laughing like a maniac as a boulder the size of a small house was suddenly rendered into chips tinier than pebbles.

"You're just jealous because I'm a better hero than you!" Alex teased, bellowing happily into her earpiece as she quickly flew off to find something else to absolutely obliterate.

"You are not!" Kara snapped, but Alex could hear the childish pout in her voice and it made her laugh.

"Little sister is getting jealous!" Alex sing-songed as she, just for fun, drop-kicked another boulder into dust particles. Man, what a rush!

"Am not," Kara grumbled, but since Alex now had heightened hearing thanks to the Harun-El, she heard this remark from Kara and laughed again.

"Listen!" Kara cried. "Even with all your training, and time with the DEO, you still don't have my experience fighting baddies one-on-one!"

"Pah!" Alex snorted. "Even though you are right about that, realize that I'm still physically stronger than you ever were and that any baddies dumb enough to cross me probably aren't going to live long enough to even engage in a real battle with me!" she continued to brag, and here was one place where she had a point. Though maybe it wasn't quite so accurate for her to claim that she was stronger now than Kara had ever been, it was true that Alex, hypothetically, could reach that point...

As strong and powerful as Kara was, Alex had far more formal training in the art of war. As such, with the Harun-El boost, Alex wasn't just getting increased strength, all of her skills and training were following after. If Kara had also been in tip-top shape and if the two sisters would've duked it out, Alex would be able to hold her own fairly well. Kara would most likely win because she was more used to being a Kryptonian than Alex, but Alex would definitely be a hard opponent to beat. She had more training than Kara, and more experience in coming up with fighting tactics outside of brute strength alone. Kara might've been physically unstoppable, but if she were to meet a more experienced match, it would be the end of her. And if Alex ever got time to get as used to being a Kryptonian as Kara already was, then there was no doubt in either of their minds that Alex would prove to be the superior, stronger Kryptonian.

"I just hope it never gets to that point!" Kara muttered, once again forgetting that Alex could hear every word she said. Alex smirked to herself but said nothing, choosing instead to raze the landscape with all of her newfound destructive powers. She had never felt more empowered! Soaring through the sky, burning the ground to ash with her laser vision before freezing it right back up with one simple exhale! She felt like a goddess! It was the coolest thing ever! Alex wasn't just on cloud nine, she was soaring far beyond it and having the time of her life all the while! She honestly almost didn't want Kara to ever recover, mean as that sounded. But it was just too fun! Getting to just rock out and enjoy all of these new special abilities! What more could a seasoned DEO agent want?!

But it was not all fun and games. Just as Alex had told Kara many, many times before, now it was Kara's turn to tell Alex.

"You do have a real job to do, remember," the younger sister reminded the older.

"I know, I know," Alex moped, obediently flying back to National City. Once she reached the border, she activated her image inducer. It was given to her so that she would look just like Supergirl. Since the world wasn't supposed to know that the real Girl of Steel was out sick, this temporary replacement was given an image inducer to copy her appearance perfectly. Kara personally found it really weird to essentially be watching herself flying through the city even though she was currently confined to the DEO, but she understood the logic behind Alex using an image inducer to mimic her appearance. For that, she said nothing as Alex returned to the city, wearing her face.

But even though Alex had Kara's look and mannerism down pat, Kara's natural grace, skill and ability still needed a bit of work... As mighty as Alex was, and as fast a learner as she was, she was not perfect. The proof came into how much she struggled with controlling Kara's powers, now that she was back in a city and thusly confined by more rules and regulations than if she had just stayed out in the middle of nowhere. She even almost crashed into about six buildings a mere four minutes after returning to the city.

"Really? And you wanted to ever criticize me?" Kara snorted, torn between amusement and mortification as Alex skimmed the roof of L-Corp, taking off a layer of mortar with her. The roof did not gain a hole, thankfully, but there was now a long, deep rut in it. Kara cringed, but she still took the opportunity to make a jibe at Alex, referencing their olden days when Kara was first learning the Kryptonian ropes herself.

In those early days, Alex had been in Kara's shoes, studying the DEO's large monitor to keep an eye on Kara's surroundings while Kara, herself, attempted to get her powers under control.

"It's not as easy as it looks!" Alex defended embarrassedly as she wiped bits of mortar from her now-long, glowing locks of gold.

"Oh how the turns have tabled," Kara joked dryly as she watched Alex continue to fly awkwardly along over the city.

"Shut up," Alex replied with a pout, which only earned another snort of laughter from Kara. Shaking her head, then, Alex carefully angled her body upward and brought herself higher. That way, she wouldn't be in danger of crashing into anymore buildings. And hopefully, since she was higher up now, there would be no one around to see anymore of her potential blunders. Minus Kara, of course. Alex inwardly groaned in embarrassment that Kara should get such a nice front-row-seat view of all of her Kryptonian blunders.

"Your flying is crooked," Kara remarked at last as Alex tried to move in and out of the clouds. "And honestly, I've seen pigeons flying with more grace and speed than you right now!" she added with a smirk as she continued to observe her sister's flying skills (or lack thereof).

"Hey! No one likes a back-seat flyer!" Alex pouted.

"I'm not a back-seat flyer!" Kara replied. "I'm your instructor!"

"Ok, Drill Sergeant J'onzz," Alex grumbled back, but she did her best to steady and even herself back out again.

After a while, then, Kara decided to test Alex's superpower control. Now that they were in the city, she had to be a bit more careful than before, and could not afford to be quite so reckless or free now that she was surrounded by thousands and thousands of people.

"Try burning a hole in the cloud in front of you!" Kara said at one point, pointing to a large, fluffy white cloud floating about 10 feet in front of Alex. This task wouldn't just test Alex's ability to use and aim her laser eyes, it would test her ability to control and move them as well, focusing more on finesse instead of basic usage.

"Ok!" Alex replied, eager to prove herself worthy. She was able to get the laser vision started and she actually had a very powerful beam of energy going, but unfortunately, she still wasn't very good at moving that beam. One slight eye-movement too far and that entire jet of burning light went off course and slashed through the cloud in front of her all the way to the one at her left shoulder.

"Hmmm," Kara mused as she looked at the destruction Alex's laser vision had caused to the clouds. "Your heat vision isn't hot enough."

"Kara!" Alex pouted, knowing that Kara was just being mean now. Although Alex's attempt at controlling her newfound laser vision had been pretty bad (thank god there were no planes nearby, or she would've accidentally cut it in half), it was not because of the strength or heat (or supposed lack thereof). Instead, it had all been a matter of control, and not moving her eyes too fast in case she accidentally whipped around again and fried far more than just her intended target.

"Try your freeze breath next!" Kara suggested. That was a little bit less dangerous just because it couldn't shoot as far as the laser eyes. Alex made a noise of uncertainty, but she obliged and flew towards one of the clouds with a giant hole now in it because of her laser vision mishap. She exhaled gently over it, trying to patch the cloud back up with her own ice. It worked fairly well, or least she thought it had.

"No," Kara critiqued again, but the lilt in her voice made it clear that although her complaint was valid, she was still just trying to get Alex's goat at this point, being unnecessarily picky with her just because that was what sisters did with each other. "Your ice-breath range is too broad, you accidently froze way more than your intended target. The entire cloud got bigger. You didn't just patch up the hole."

"Grrr," was Alex's semi-playful reply. Although she knew full well Kara was just trying to get back at her for all the times she'd been the one to nag the Kryptonian, that didn't mean that some of her remarks didn't really get under Alex's now-invulnerable skin.

At last, though, Alex decided to dip back down below the clouds and closer towards the city again.

"Don't crash into anymore buildings," Kara warned teasingly and Alex flipped her off, knowing exactly where the camera was on her body so that Kara could see the message loud and clear. Alex knew it was properly sent and received when she heard Kara burst with laughter.

"Real mature!" Kara laughed as Alex's middle finger filled up the entire screen, since Alex had pressed it so close to the camera.

But then some real adventure finally did decide to happen.

"Oh, finally! Thank god!" Alex cried in genuine relief as and Kara were both alerted to a robbery happening at a store on main street. Alex wasted no time in speeding over to the store, but she flew in so fast that when she landed, she only just barely missed smashing right through the store.

"You're trying to save a store, not demolish it!" Kara complained, slapping her forehead as she watched Alex's very, very, shaky and abrupt landing. It was the flying equivalent of slamming on the breaks to properly stop at a red light. That was heart attack central for Kara right there.

"Let's see you do better!" Alex grouched embarrassedly, sensing that Kara's dismay with her was real this time. But the second she tried to defend herself with this question, she realized how stupid she had sounded. But it was too late, Kara was already replying. Oh, joy of joys...

"Did you really just say that? To me? The original Girl of Steel?" Kara snorted, a tiny bit of humor returning to her voice as she dared to look at the screen once again. There were two giant potholes under Alex's feet now, but at least the store was still all in one piece.

"I hate you," Alex grunted softly into her earpiece.

"You too, sis!" Kara replied, and Alex could hear that smug little grin in her younger sister's voice. Kara was really getting her sweet, sweet revenge for all of Alex's nagging and she was loving every single second of it.

But with the robbery currently going on, the sisterly banter had to be put aside. Alex did her best to copy Kara's "Supergirl stance", with the raised chin, proud eyes and hands on hips, and it worked fairly well. The robbers stopped dead in their tracks, all of them looking some degree of afraid of Supergirl. Alex couldn't stop a tiny, tiny huff of laughter from escaping from her lips. God, it felt so good to be this powerful and intimidating! She could already be really scary all on her own, but to have the Harun-El boost mixed with a Supergirl image inducer took it to the next level and created what had been, up until today, nothing more than a guilty and stupid little fantasy of Alex's. But now it was a reality! She got to scare the pants off of criminals by being the legendary Girl of Steel!

But as with all criminals, no matter whether they were human or alien, they refused to come quietly, even if logic dictated that a peaceful and quiet surrender would be the best course of action. Instead, a few of the braver ones opened fire on Alex, but of course, with all that Harun-El in her veins, every single bullet bounced harmlessly off of her.

"You think they would know better!" Alex snorted as she continued to stand with her hands on her hips, chest puffed up proudly.

"I know, right?!" for a moment, Kara forget her embarrassment with how poorly Alex was controlling her "Kryptonian" body to agree with her about robbers' stupidity. Everyone knew Kryptonians were invulnerable to bullets, and yet still, every criminal Kara ever faced tried to shoot her.

"Ok, that's enough of that now, I'm getting tired, and you're wasting a perfectly good load of ammo!" Alex snarked, strutting right up to the first criminal and easily yanking the gun from his hand. She didn't even need to try in order to flatten it like a pancake in her hand.

"Oh! Be careful Alex!" Kara's worrying side returned. She knew all too well about how easy it was to forget how strong she was as a Kryptonian. If Alex wasn't cautious and aware at all times, she could so easily accidentally kill these criminals. After all, Kara had needed to practice for weeks with being gentle enough to safely touch a human. Alex would have to reign in if she wanted to not accidentally kill these criminals.

"Ah, right," Alex muttered embarrassedly as she tried to not touch anything too hard or too fast. It really did feel weird to her to have to fight so "delicately" and reign in. As a DEO agent, she was used to going all-out in battle, pulling no punches and holding nothing back. But here, she had to be gentle and hardly even touch anything, lest she accidentally cause some major damage. It just felt so weird and wrong to her and she didn't like it at all. She liked the feeling of kicking and punching and going berserk, but she couldn't do that anymore. Not while she was all jacked up on the mythical, mystical Kryptonian steroid known as Harun-El.

In the end, Alex finally just scooped all of the robbers up by their feet (being careful not to crush any of them while she held onto them) and carried them a few feet off the ground. It rendered them immobile and terrified. Even if she dropped them, the fall would not be fatal, but they still hated being held up by their ankles by an angry Kryptonian. The whimpered and whined, begging for mercy, and begging to be put down again, but Alex only serenely shook her head.

"Not until the cops come!" she sing-songed, and she waited until she caught sight of the first car before she put any of the criminals down again.

"Thanks, Supergirl!" one of the cops said, not realizing he was speaking to Supergirl's older sister.

"No problem," Alex replied with a confident smile as she finally set the criminals back down on the ground. They were arrested at once. But some time during all of this, Maggie Sawyer stepped onto the scene and, just for a second, Alex felt her face flushing. She stared long and hard at the beautiful officer and realized that she quite liked seeing Maggie with her new superpowered eyes...

"Stop using your X-ray vision to see through Maggie's clothes!" Kara's voice suddenly filled her head and caused her to literally jump up into the air, surprised and embarrassed both at being caught and interrupted.

"Jesus, Kara!" Alex whined as she tried to look like she hadn't just been spooked. Kara only snickered on the other side of the coms.

"Just come on back to the DEO, you lovesick, lovestruck doofus!" the original Supergirl told her temporary replacement.

"Grrr," was Alex's reply again, but she still obeyed and took back to the sky again, though Kara caught her staring at Maggie for as long as Maggie was in her direct line of sight. Of course, this slightly backfired about a minute later when Alex got high enough up and-

"Oh my Rao, Alex!" Kara sighed into her hands as Alex flew straight through a cloud and came out the other side soaking wet. Alex was too embarrassed to reply, trying to hold onto her dignity through silence, and a stoic expression. Although she really did find being superpowered to be really fun and cool, realizing how inexperienced she was at controlling all these newfound abilities was quite embarrassing for her. She felt like an infant just learning to walk again and she hated feeling that stupid, useless, powerless and helpless. And Kara's embarrassment and exasperation over having to watch Alex make so many blunders was not helping.

Kara, meanwhile, was taking deep breaths to calm herself down (though some of those breaths were kind of heavy, because of the illness coursing through her body). Although she loved Alex dearly and was over the moon to see her sister finally getting a chance to be Super, this was just painful to watch. Of course, she understood that Alex would need a lot of training to master the art of being Kryptonian, but that didn't make it fun for Kara to watch. Alex once again tried to veer around a cloud only to upset a flock of geese flying overhead.

"Oh! Shoot!" Kara's earpiece was suddenly filled with profanities as Alex cussed out her surprise, irritation and embarrassment at slamming headfirst into a flock of geese. By some miracle, none of them were killed by Alex crashing through their ranks, but they all honked in fright and surprise, scrambling to get away from the clumsy disaster that was Alexandra Danvers.

"Gah! Sorry!" Alex shouted as she managed to finally escape the geese. They continued to honk as they flew away, quickly able to reform ranks. That, at least, made Alex a bit better. She was glad to know none of them had been harmed (or killed) by her mistakes and inexperience.

"Want to knock it back down to a PG level there, Alex?" Kara asked as Alex brushed the last of the feathers off of her super suit, her cussing finally ceasing now that the wild goose chase was over.

"Oh, shut up," Alex grumbled back.

"Well remember, as the Girl of Steel, you aren't supposed to have a sailor's mouth!" Kara snickered.

"Oh, cry me a river!" Alex retorted, and on she flew back towards the DEO. But of course, one more almost-mistake had to happen first...

"Watch out for that lamppost!" Kara shrieked as Alex nearly flew straight into one. Alex managed to jerk her body out of the way in the nick of time... before slamming right into a stop sign on the opposite side of the road. Talk about overcompensating on a turn!

"Ouch!" Alex grunted in embarrassment, even though she hadn't felt the impact at all. But the sign certainly had! It had been uprooted from the ground and bent in half, the actual sign-piece having been broken in half. One half was still attached the pole (even if only by a proverbial thread) while the other half had been smashed deep into the sidewalk.

"Urgh!" Kara groaned again, shaking her head as she buried it into her hands once more. Alex felt herself blushing hotly. She was so close to the DEO and yet she still had to make one more flight crash. This must've been how SpongeBob felt trying to drive a boat around Biking Bottom, only to crash into every building along the way, even if it should've been an easy-to-miss situation.

After that, Alex just walked home, entering the DEO on foot. Despite all the awkwardness of trying to be a Kryptonian and despite all of her past mistakes, though, Alex felt genuinely happy. She felt strong, powerful and successful. And even though she had suffered a few mistakes (at one point during her battle with the robbers, she'd fried a hole into the ground with her eyes before accidentally freezing every car on the block onto the street in attempt to put out the fire started by her laser vision) she had still technically stopped the bad guys. And the citizens had been quick enough to forgive her, despite her nearly burning down the store and then freezing their cars to the road.

Luckily, though, the DEO had sent out other agents to use flamethrowers to carefully melt all the ice from the road. With any luck, the traffic delay wouldn't be too long and nothing else would catch alight. Alex had felt bad about making the other agents clean up her mess, but they assured her that it was problem best if she just went back to the DEO and regroup. Heaven knew they weren't about to let her use her laser eyes to try and melt the ice! And they didn't exactly trust her with a flamethrower, especially not at a time like this...

It was clear that Alex found all of this a bit embarrassing and disappointing, to have all of these amazing powers and yet none of the skills needed to use them safely, but she was willing to put away her ego for the sake of the city and not try anything else, just in case it caused another disaster. No one needed that. Alex was already sure that Lena would rake her over the coals for nearly destroying the top floor of her building (which was also her office, hence why Alex was so worried that Lena was going to be pissed). But Kara and the other DEO agents back at the base gave Alex a warm reception, genuinely applauding her and all of her efforts and good deeds over the past 12-ish hours. No matter how mistakes Alex had made, she had done well for a first time, and she had technically saved the day. Even if it was a messy, rocky start, it was a start nonetheless and all of her friends were incredibly proud of her. Alex had never felt happier. Being cheered and clapped for like this felt amazing!

But in time, the fun had to end. Kara's mysterious bug passed and with each passing minute, she grew happier, healthier, stronger and better. One by one, all of her powers returned until she was back to her good old self once more, fully restored to top condition.

"I'm back, baby! I! AM! BACK!" she cheered, hooting and hollering as she literally flew laps around the DEO.

"Showoff," Alex grumbled as her own powers began to wane. The Harun-El was wearing off and with Kara ready to take up her job again, there was no need to give Alex another dose of it. The thought saddened her because even though she was still a disaster in a cape while high on the Harun-El, she had been getting much better at being a Kryptonian and now all of that was going to go away again. Being a superhero really had been fun, and Alex was sad to see that life slip away from her once again.

"Awww, don't you worry, sis, I thought you made a great Supergirl!" Kara promised Alex, finally coming down to comfort her sister.

"Yeah right," Alex snorted. Even though it still wounded her pride to admit how bad she'd been at being a Supergirl, she couldn't deny that it had been pretty awful. But this time, Kara refused to agree.

"No, really, you were great," she promised. "And I'm not just saying that to make you feel better!" she added, when Alex gave her a look. "I mean think about it: sure you didn't exactly have a great start, but to learn how to fly and use all my powers passably well in under a week? That's incredible! It took me a lot longer than that to master the art of being a Kryptonian, yet you managed to learn it all in like five days!"

Kara continued to try and get Alex to see just how amazing she really had been and, after long enough, it began to work.

"Yeah, I was a pretty fast learner, wasn't I?" Alex finally cracked a smile for the first time in days.

"Faster than the Flash!" Kara promised back, squeezing Alex gently. "And heck, I'm sure that if you'd been given more time to get used to being Super, you would've become even stronger than me!" she added, and that was a compliment so high and so personal that even Alex looked taken aback by it. Admittedly, Kara did sometimes get a bit of an ego, and she absolutely hated being weak or powerless, so to hear her willingly say that Alex would ever be stronger than her was beyond astounding. But again, she was not necessarily wrong. Even though Kara was more used to being a Kryptonian, Alex had far more formal training in combat. If Alex had had more time under the Harun-El, who knows what she could've become?

"Wow, you're right!" Alex murmured at last, sounding genuinely pleased and proud of herself for once. It made Kara smile. She knew about Alex's self-esteem issues and she hated to think that she and her powers were partly the reason for it. That was why Kara was working so hard to get Alex to see how special she already was, human or Kryptonian. At long last, then, Kara finally succeeded in her goal, and she put Alex's mind at ease, having successfully gotten her to realize that her worth had not diminished at all just because she was no longer a Girl of Steel.

"Besides, I think you do a better job at being the naggy copilot than I do," Kara teased.

"What?" Alex sat up straighter, an indignant frown upon her face. "I wasn't that naggy!"

"Oh yes you were!" Kara snorted back.  
"Was not! I was only trying to help!" Alex defended herself. "You nagged me just to get even, but I was only ever trying to help you!"

"Well, then so was I!" Kara shot back, but she was smiling through it all. "Maybe I was just trying to help you too, you know? Because Rao knows you certainly needed all the help you could get!"  
"No, you were just being mean and you know it!" Alex pouted.  
"Well, it wasn't as mean as all your criticisms of me in the past!" Kara snapped back without missing a beat.  
"No, you were way worse!" Alex shook her head with a sharp laugh. And on and on the two sisters bickered, just as any good and realistic pair of siblings did. But even though their petty little fights, there was laughter and warmth between the two of them, and by the end of the fight, the two managed to come to a compromise...

"Absolutely not! You are never allowed anywhere near Harun-El again," Kara said at last, and Alex couldn't help but laugh.

"Ok, ok," she surrendered finally. "Maybe I'll leave the Super stuff to you."

"Good idea," Kara snorted, but then her face softened. She knew how much it meant to Alex to be able to be a Kryptonian, even if only for a little.

"Actually, there is one Super job that I'm leaving up to you," she said quietly, trying to make up for having to take her sister's fun away.

"Oh?" Alex gave Kara a genuinely surprised and interested look.

"Yeah," a teeny smile flickered across Kara's face. "The job of being my Super Sister."

"You dork," Alex laughed, but she felt a rush of affection for Kara surge through her heart.

ooo

A week later, though, Kara's first promise about Alex and the Harun-El fell through. From that day on, sometimes the other DEO agents would catch not one, but two, Kryptonians flying around the DEO training room together. There were plenty of messes and accidents, but they were always followed by hugs, laughter and words of encouragement.

"Good job, Super Sister," Kara grinned, slapping Alex on the back as she finally managed to hit her intended target with her laser vision. That was one of the best parts about both of them being superpowered, Kara no longer had to be gentle with Alex, but instead, she could be as rough, feely, physical and emotional as she wanted. So no longer had to hold back or go easy and, in her mind, that was the very best part about all of it.

Alex, meanwhile, grinned proudly before slapping Kara right back with the same amount of force (which would've been strong enough to knock over a semi).

"And it was all thanks to you, Super Sister!" she said, and the rest of the day passed by in a blur of love, light and laughter.

**Author's Note:**

> AN: Ok, ThatChickenHead, here's your "Alex gets a Harun-El" boost fic. Hope you liked it!
> 
> Also, just like so many times before, shout out to Snorlax891, some of our previous convos did inspire parts of this fic.


End file.
